Ventilation is a primary engineering control method for directly reducing potential hazards from airborne contaminants during work in confined spaces (CS). However, there is not enough information available on how to design CS ventilation or to assist in evaluating ventilation effectiveness. The results of the proposed study will provide useful "tools" for planning and implementing effective CS ventilation strategies. The specific Aims of the proposed research are to: 1. Measure ventilation effectiveness of CS models by simulating "contaminant" release and determining the air mixing factor, K, for equations which describe dilution ventilation. Primary test parameters will be: o CS configuration (open-top vessel, closed vessel with one or two openings, size and shape variations). o Ventilation scheme (volume flowrate variations, air supply and/or exhaust, inlet/outlet elevation) o Contaminant" characteristics (uniform diffusion/dispersion, heavier-than-air, oxygen deficiency, "continuous" release, and "purging"). 2. Investigate ventilation characteristic for CS models -- percentage of contaminant" reduction, airflow velocities, and "smoke" visualized airflow patterns. 3. Develop a computer design model for CS ventilation to predict required ventilation flowrates, design guidelines, and recommendations for ventilation evaluation. 4. Conduct field testing and field scale model testing to evaluate the modeling approach and validate the computer design model.